The content created by the users of social networking sites has reached such high levels of quality and variety that it is comparable to that produced by professional agencies. Therefore, understanding what types of content users generate and the underlying motivational factors is vital to the success of the sites. The extant research on content generation has primarily focused on the amount of content and on how to encourage participation in content creation, and less attention has been paid to the content itself and how social relations affect the types of content that users upload. This study aims to empirically document the relationship between social ties and the similarities between the types of content that people create online. We collected a large data set from the photo-hosting website Flickr detailing the users' social relations over time in conjunction with their photo-uploading behavior. We found that around the time of the formation of a social tie, members of dyads began to upload more similar photos than they did before that time. After a social tie was formed, this similarity evolved in different ways in different subgroups of dyads. Whereas the similarity between photos uploaded by dyads experiencing notably different popularity levels on the site continued to grow, the dyads of users with similar levels of popularity gradually began to upload less similar photos. In cultural production, individuals appear to present themselves as unique; this feature is more salient when the social contacts are similar in popularity status. Photo-shooting behaviors have been found to exhibit the same patterns. Furthermore, we show that the most divergent uploading behavior is observed when a high-popularity user initiates a tie with a user with lower popularity. We use social psychological motivations to explain these results.